1. Technical Field
The present disclosure relates to a pan tilt drive device and a camera device.
2. Description of the Related Art
Some camera devices are provided with a pan tilt drive device, thereby enabling a camera body to capture an image in a desired direction through pan rotation and tilt rotation. This type of camera device rotates the camera body by using a reduction mechanism to decelerate rotation of a motor. Some camera devices have a preset function to store an imaging direction set by a user so that the camera body automatically faces in the imaging direction. If the camera device provided with the preset function receives a preset instruction, the camera device drives the motor, and transmits rotation of the motor while using the reduction mechanism to decelerate the rotation of a motor. A housing which accommodates the camera body for a camera base performs pan rotation or tilt rotation, or performs both the pan rotation and the tilt rotation so that the camera body is directed toward a desired preset position.
As the related art in which the reduction mechanism is applied to the camera device (for example, a monitoring camera), a reduction gear is known which is provided with a backlash removal function disclosed in Japanese Patent Unexamined Publication No. 2007-170459. The reduction gear provided with the backlash removal function includes a first internal gear which is stationary, a second internal gear which is rotatable, and two planetary pair gears coaxially having a first external gear and a second external gear. The first external gear of the planetary pair gear meshes with the first internal gear, and the second external gear meshes with the second internal gear. A reduction ratio difference is established between a reduction ratio of the first internal gear and the first external gear and a reduction ratio of the second internal gear and the second external gear, and a rotation drive force is input to the reduction gear. If the planetary pair gear revolves while being rotated, the rotation drive force reduced in accordance with the reduction ratio difference is output from the reduction gear. In this case, the second internal gear is directed toward a gear match point between the first internal gear and the second internal gear. Torsional stress is received from both sides, and a backlash is removed.
However, the reduction mechanism transmits the rotation by meshing with a plurality of gears. Consequently, accuracy in a rotation transmission amount may be degraded due to a clearance (backlash) between the gears. In this case, a problem arises in that accurate positioning at the preset position cannot be performed. In a case where the reduction ratio is obtained by a pair of gears meshing with each other, it is relatively easy to restrain the backlash. In this case, the gears mesh with each other on the same plane. Thus, a clearance between tooth surfaces can be reduced by displacing the gears in a direction within a single plane.
However, in a case of a dual stage reduction mechanism in which two gear sets mesh with each other in order to obtain a greater reduction ratio, the gears may mesh with each other on mutually different planes. In this case, since Japanese Patent Unexamined Publication No. 2007-170459 adopts a configuration in which a single stage reduction mechanism reduces the backlash, it is difficult to reduce the clearance between the tooth surfaces by concurrently displacing the two gear sets. In view of these circumstances, the camera device provided with the dual stage reduction mechanism is also required to improve position accuracy of a preset operation.